Solar Cell Essay Example For Students

Solar Cell Essay Solar cellsSolar cells today are mostly made of silicon, one of the most commonelements on Earth. The crystalline silicon solar cell was one of the firsttypes to be developed and it is still the most common type in use today. They do not pollute the atmosphere and they leave behind no harmful wasteproducts. Photovoltaic cells work effectively even in cloudy weather andunlike solar heaters, are more efficient at low temperatures. They do theirjob silently and there are no moving parts to wear out. It is no wonderthat one marvels on how such a device would function. To understand how a solar cell works, it is necessary to go back tosome basic atomic concepts. In the simplest model of the atom, electronsorbit a central nucleus, composed of protons and neutrons. each electroncarries one negative charge and each proton one positive charge. Neutronscarry no charge. Every atom has the same number of electrons as there areprotons, so, on the whole, it is electrically neutral. The electrons havediscrete kinetic energy levels, which increase with the orbital radius. When atoms bond together to form a solid, the electron energy levels mergeinto bands. In electrical conductors, these bands are continuous but ininsulators and semiconductors there is an energy gap, in which noelectron orbits can exist, between the inner valence band and outerconduction band Book 1. Valence electrons help to bind together the atomsin a solid by orbiting 2 adjacent nucleii, while conduction electrons,being less closely bound to the nucleii, are free to move in response to anapplied voltage or electric field. The fewer conduction electrons there are,the higher the electrical resistivity of the material. In semiconductors, the materials from which solar sells are made, theenergy gap Eg is fairly small. Because of this, electrons in the valenceband can easily be made to jump to the conduction band by the injection ofenergy, either in the form of heat or light Book 4. This explains why thehigh resistivity of semiconductors decreases as the temperature is raisedor the material illuminated. The excitation of valence electrons to theconduction band is best accomplished when the semiconductor is in thecrystalline state, i.e. when the atoms are arranged in a precisegeometrical formation or lattice. At room temperature and low illumination, pure or so-calledintrinsic semiconductors have a high resistivity. But the resistivity canbe greatly reduced by doping, i.e. introducing a very small amount ofimpurity, of the order of one in a million atoms. There are 2 kinds ofdopant. Those which have more valence electrons that the semiconductoritself are called donors and those which have fewer are termedacceptors Book 2. In a silicon crystal, each atom has 4 valence electrons, which areshared with a neighbouring atom to form a stable tetrahedral structure. Phosphorus, which has 5 valence electrons, is a donor and causes extraelectrons to appear in the conduction band. Silicon so doped is called n-type Book 5. On the other hand, boron, with a valence of 3, is anacceptor, leaving so-called holes in the lattice, which act likepositive charges and render the silicon p-typeBook 5. The drawings inFigure 1.2 are 2-dimensional representations of n-and p-type siliconcrystals, in which the atomic nucleii in the lattice are indicated bycircles and the bonding valence electrons are shown as lines between theatoms. Holes, like electrons, will remove under the influence of an appliedvoltage but, as the mechanism of their movement is valence electronsubstitution from atom to atom, they are less mobile than the freeconduction electrons Book 2. .ua41da4533b65f2f6d358cb4a049fbb06 , .ua41da4533b65f2f6d358cb4a049fbb06 .postImageUrl , .ua41da4533b65f2f6d358cb4a049fbb06 .centered-text-area { min-height: 80px; position: relative; } .ua41da4533b65f2f6d358cb4a049fbb06 , .ua41da4533b65f2f6d358cb4a049fbb06:hover , .ua41da4533b65f2f6d358cb4a049fbb06:visited , .ua41da4533b65f2f6d358cb4a049fbb06:active { border:0!important; } .ua41da4533b65f2f6d358cb4a049fbb06 .clearfix:after { content: ""; display: table; clear: both; } .ua41da4533b65f2f6d358cb4a049fbb06 { display: block; transition: background-color 250ms; webkit-transition: background-color 250ms; width: 100%; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #95A5A6; } .ua41da4533b65f2f6d358cb4a049fbb06:active , .ua41da4533b65f2f6d358cb4a049fbb06:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #2C3E50; } .ua41da4533b65f2f6d358cb4a049fbb06 .centered-text-area { width: 100%; position: relative ; } .ua41da4533b65f2f6d358cb4a049fbb06 .ctaText { border-bottom: 0 solid #fff; color: #2980B9; font-size: 16px; font-weight: bold; margin: 0; padding: 0; text-decoration: underline; } .ua41da4533b65f2f6d358cb4a049fbb06 .postTitle { color: #FFFFFF; font-size: 16px; font-weight: 600; margin: 0; padding: 0; width: 100%; } .ua41da4533b65f2f6d358cb4a049fbb06 .ctaButton { background-color: #7F8C8D!important; color: #2980B9; border: none; border-radius: 3px; box-shadow: none; font-size: 14px; font-weight: bold; line-height: 26px; moz-border-radius: 3px; text-align: center; text-decoration: none; text-shadow: none; width: 80px; min-height: 80px; background: url(https://artscolumbia.org/wp-content/plugins/intelly-related-posts/assets/images/simple-arrow.png)no-repeat; position: absolute; right: 0; top: 0; } .ua41da4533b65f2f6d358cb4a049fbb06:hover .ctaButton { background-color: #34495E!important; } .ua41da4533b65f2f6d358cb4a049fbb06 .centered-text { display: table; height: 80px; padding-left : 18px; top: 0; } .ua41da4533b65f2f6d358cb4a049fbb06 .ua41da4533b65f2f6d358cb4a049fbb06-content { display: table-cell; margin: 0; padding: 0; padding-right: 108px; position: relative; vertical-align: middle; width: 100%; } .ua41da4533b65f2f6d358cb4a049fbb06:after { content: ""; display: block; clear: both; } READ: Columbian Exchange EssayIn a n-on-p crystalline silicon solar cell, a shadow junction isformed by diffusing phosphorus into a boron-based base. At the junction,conduction electrons from donor atoms in the n-region diffuse into the p-region and combine with holes in acceptor atoms, producing a layer ofnegatively-charged impurity atoms. The opposite action also takes place,holes from acceptor atoms in the p-region crossing into the n-region,combining with electrons and producing positively-charged impurity atomsBook 4. The net result of these movements is the disappearance ofconduction electrons and holes from the vicinity of the junction and theestablishment there of a reve rse electric field, which is positive on then-side and negative on the p-side. This reverse field plays a vital part inthe functioning of the device. The area in which it is set up is called thedepletion area or barrier layerBook 4. When light falls on the front surface, photons with energy in excessof the energy gap (1.1 eV in crystalline silicon) interact with valenceelectrons and lift them to the conduction band. This movement leaves behindholes, so each photon is said to generate an electron-hole pair Book 2. In the crystalline silicon, electron-hole generation takes place throughoutthe thickness of the cell, in concentrations depending on the irradianceand the spectral composition of the light. Photon energy is inverselyproportional to wavelength. The highly energetic photons in the ultra-violet and blue part of the spectrum are absorbed very near the surface,while the less energetic longer wave photons in the red and infrared areabsorbed deeper in the crystal and further from the junction Book 4. Mostare absorbed within a thickness of 100 m. The electrons and holes diffuse through the crystal in an effort toproduce an even distribution. Some recombine after a lifetime of the orderof one millisecond, neutralizing their charges and giving up energy in theform of heat. Others reach the junction before their lifetime has expired. There they are separated by the reverse field, the electrons beingaccelerated towards the negative contact and the holes towards the positiveBook 5. If the cell is connected to a load, electrons will be pushed fromthe negative contact through the load to the positive contact, where theywill recombine with holes. This constitutes an electric current. Incrystalline silicon cells, the current generated by radiation of aparticular spectral composition is directly proportional to the irradianceBook 2. Some types of solar cell, however, do not exhibit this linearrelationship. The silicon solar cell has many advantages such as high reliability,photovoltaic power plants can be put up easily and quickly, photovoltaicpower plants are quite modular and can respond to sudden changes in solarinput which occur when clouds pass by. However there are still some majorproblems with them. They still cost too much for mass use and arerelatively inefficient with conversion efficiencies of 20% to 30%. Withtime, both of these problems will be solved through mass production and newtechnological advances in semiconductors. Bibliography1) Green, Martin Solar Cells, Operating Principles, Technology and SystemApplications. New Jersey, Prentice-Hall, 1989. pg 104-1062) Hovel, Howard Solar Cells, Semiconductors and Semimetals. New York,Academic Press, 1990. pg 334-3393) Newham, Michael ,Photovoltaics, The Sunrise Industry, Solar Energy,October 1, 1989, pp 253-256 4) Pulfrey, Donald Photovoltaic PowerGeneration. Oxford, Van Norstrand Co., 1988. pg 56-615) Treble, Fredrick Generating Electricity from the Sun. New York, PergamonPress, 1991. pg 192-195

Mr Khan free essay sample

Assume the room is well sealed and heavily insulated. 2. An ideal Otto cycle has a compression ratio of 9. 2 and uses air as the working fluid. At the beginning of the compression process, air is at 98 kPa and 27oC. The pressure is doubled during the constant-volume heat-addition process. Accounting for the variation of specific heats with temperature, determine (a) the amount of heat transferred to the air, (b) the net work output, (c) the thermal efficiency, and (d) the mean effective pressure for the cycle. . A gas turbine power plant uses solar energy as the source of heat addition (see Figure for detailed setup and operating data). Modelling the cycle as a Brayton cycle and assuming no pressure drops in the heat exchanger or interconnecting piping, determine: (a) the thermal efficiency; (b) the air mass flow rate, in kg/s, for a net power output of 500kW. 4. Steam is the working fluid in an ideal reheat Rankine cycle. We will write a custom essay sample on Mr Khan or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Steam enters the first-stage turbine at 8. 0 MPa, 480oC, and expands to 0. 7 MPa. It is then reheated to 440oC before entering the secondstage turbine, where it expands to the condenser pressure of 0. 008 MPa. The net power output is 100 MW. Determine (a) the thermal efficiency of the cycle, (b) the mass flow rate of steam, in kg/h, (c) the rate of heat transfer out from the condensing steam as it passes through the condenser, in MW. Discuss the effects of reheat on the vapor power cycle. NOTE: Do the problems in a systematic way. Include the units in the calculations. State any assumptions.

The Microsoft Antitrust Case essays

The Microsoft Antitrust Case essays The case against Microsoft was brought buy the U.S. Department of Justice, as well as several state Attorneys General. Microsoft is accused of using and maintaining monopoly power to gain an unfair advantage in the market. The case has been under observation for a long time, but the Justice department is having trouble coming up with substantial evidence against Microsoft. Specifically, the Department must prove: That Microsoft has monopoly power and is using it to gain unfair leverage in the market. And that Microsoft has maintained this monopoly power through exclusionary or predatory acts(Rule). Some say that Microsoft is only taking advantage of its position in the market and using innovative marketing strategies to attract new customers. They have chosen to implement a market development strategy to attract new customers who are looking for a system that has Internet capability. Microsoft feels that by integrating their Internet Explorer web browser technology into Windows, they are only improving its overall functionality available to the customer. Microsoft began expanding into the browser area because of increasing threat from Netscape and Java. Java is the programming language used to make Netscape. Programs that are written in Java can work on any PC, whether it has Windows on it or not. That is why there is a great threat to the Windows environment. The more Netscape is used, the more other vendors will begin writing Netscape compliant programs and the more Java will be used, which puts a damper on Windows. So Windows introduced their Internet explorer to combat the increasing Netscape usage. It did not do this to create a monopoly, but to protect itself. If people realize that Java programs can be run on ANY PC, then they will realize that they do not need to buy Windows. Some say that Microsoft began its illegal̶...

West Wing Episodes Discussion Essay Example | Topics and Well Written Essays - 1000 words

West Wing Episodes Discussion - Essay Example In Episode 96 â€Å"Shutdown†, the Operating Budget of the Federal Government is   reduced to zero and the government is forced into a temporary shutdown after President Bartlett refuses to any further Budget compromises, which puts him in a very unfavorable position.   Without the operating budget, the Chief of Staff sends everyone home who is non-essential personnel, including non-national security and public safety employees.   In Episode 96 â€Å"Shutdown†, the Operating Budget of the Federal Government is   reduced to zero and the government is forced into a temporary shutdown after President Bartlett refuses to any further Budget compromises, which puts him in a very unfavorable position.   Without the operating budget, the Chief of Staff sends everyone home who is non-essential personnel, including non-national security and public safety employees.    Speaker Haftley begins turning the shutdown to his party’s favor by speaking to the press on t he White House lawn.   Press Secretary C.J. Cregg begins to recover some ground by addressing the White House Press core inside.   Meanwhile, Chief of Staff Leo McGarry attempts to talk to the President in his private quarters to convince him to sign a deal at 2 percent by midnight to stop the shutdown. But he doesn’t succeed and the shut down begins. Vice President Russell meets with McGarry and offers to speak with his former collegues in the House that includes Speaker Haftley and the Majority Whip, but McGarety refuses.

Comparing of World Views Essay Example | Topics and Well Written Essays - 750 words

Comparing of World Views - Essay Example Among some of the worldviews in contemporary society are realism, liberalism and neo-liberalism. The subsequent sections offer an in depth comparison of the worldviews in light of understanding, their impact upon individuals, cultures and nations. Realism Worldview The realist worldview holds a pessimistic ideology of state relations, global politics and peaceful cohesion. According to, Thomas Hobbes, a world renown theorist of classical realism, â€Å"Where there is no common power, there is no law; where no law, no justice. Force and law are in war with the two cardinal virtues.† Consequently, the realist worldview contends that global politics is a constant fight for power, control and position by the partisan state interests. Thus in the quest for asserting power and influence, realists believe in military strength as a benchmark. In most cases the military strength is put to test and consequently places the threat of warfare and violence on the world (Griffiths, 2012). Fu rthermore, the realist view places responsibility on states as the major factors that influence actions in the world. Moreover, the human rights of individuals are violated over state interests. According to the realist worldview, there exists a lack of higher state authority to maintain order and global peace. As a result, the world is in a constant state of anarchy and states are compelled to maintain a high level of personal protection and defense. States are in constant lookout for ways to bolster their security and boost power. Consequently, the states with greater military capacity foment and assert their strength by intimidating or attacking other states. Thus, according to this worldview, war is not only a possibility, but inevitable. In a nut shell the core tenets of realism are that global politics are defined by power over justice, the struggle for power and the balance of power results to stability. Liberal Worldview The liberal worldview takes on a more positive stance in relation to world politics, the optimism of peace and state relations. According to Dworkin, a renowned liberal theorist, equal concern and respect are the basic tenets that government should apply in governing citizens (Dworkin, 1977). Moreover, John Rawls, a famous liberal political theorist, states that the legal system of any society must ascribe to the principles of justice and fairness. Furthermore, he adds that a liberal society flourishes from the rational decision making of human beings and consequently results to good life (Rawls, 1971). The roots of liberal worldview are attributed to Immanuel Kant’s philosophy book entitled â€Å"Towards Perpetual Peace.† Kant believed that global peace was a reality through Free State federations that promote security and international order. Furthermore, he stated that an independent legislature was fundamental in checking the powers of republican governments. Consequently, the basic tenets of liberal worldview critici ze the realist worldview by emphasizing on cooperation, cohesive existence and peace in the quest for world transformation. Furthermore, the liberal worldview believes in the possibility of global cooperation in contrast to power struggles. Moreover, liberalist worldview disregards anarchy and power struggles that are hypothesized by the realist worldview. The overriding reason forwarded is the interdependence of states that shape the reality of contemporary world politics. Modern day liberal theorist such as Kymlicka, offers a refined political liberal theory in

Earning a Quality Award Research Paper Example | Topics and Well Written Essays - 500 words

Earning a Quality Award - Research Paper Example The first step that led to winning the award was the fact that the company had been consistent in offering quality services to its customers. This was in line with the requirements of the of the Malcolm Baldrige standards. Secondly, despite the company not winning the award for many years since it’s founding, they went ahead to make use of quality feedbacks received over the years from the award winners to improve their standards. Mike Frihart, a director at the company, was determined to complete applications for the award winning for several years and therefore highlighting the company’s willingness to continuously advance by regularly reviewing their performance standards. In the third step, the management adopted employee motivation schemes to encourage them to participate optimally to yield high quality products. They were rewarded with financial incentives proportionate to the company’s success, which enabled the company to retain and employ workers with sufficient skills leading to the manufacture of the best possible products. Winning an award is appreciated the world over. Winners of any kind of award get a boost and are branded as achievers in their dealings. In this context, awards have been accompanied by the following benefits: Companies that have won awards realize increase in the sales of their products because the awards act to prove validity of their products and reassure customers that the goods they consume are worthy. New customers also get influenced by this confirmation and in the long run demand for their products increases thereby improving sales. An award confirms good quality of goods/services by an organization. Through this, products/services are proved to be of required standards and the customers always feel satisfied to consuming safe goods. This is comparable to soccer scenarios. For instance, Barcelona FC has satisfied fans world over since they win awards every year. Fans,

Shabanu Essay :: essays research papers

Shabanu Essay In the novel Shabanu, by Suzanne Fisher Staples, women are portrayed in two distinct ways: obedient and rebellious. The obedient women would include Phulan, Mama, and Auntie. Rebellious women would consist of Sharma, Fatima, and, of course, Shabanu. The protagonist Shabanu, portrays herself as a rebellious woman. Shabanu constantly disobeys her father. In the beginning of the novel, Shabanu attempts to retrieve her camel Mithoo so he will not be harmed by Tipu, another camel. Dadi tells her No several times but she insists. Dadi is furious, ?Don?t ever disobey me? (27). Dadi shakes her so hard that her head flies back and fourth. Shabanu gets home and while she is making chapaties Auntie says to her, ?Shabanu, you are wild as the wind, you must learn to obey. Otherwise?I am afraid for you? (28). Another example of Shabanu?s rebelliousness is when she throws water on the landlord. Nazir Muhammad and his men say the want to ?claim? Shabanu and her sister, Phulan. Shabanu becomes disgusted and decides to throw her head forward, causing the water jug on her head to spill over the embankment and Nazir Muhammad. Sharma, Shabanu?s aunt, is a very rebellious woman as well. Sharma is described as bold, ?Most men don?t like her and are afraid of her? (98). Sharma cares about Shabanu and tries to look out for her. Although Sharma had no intentions of causing Shabanu danger, she gave her some very dangerous advice. ?You try to make him happy so he can?t bare to be away from you a single moment. If he treats you badly, come stay with us? (209). Auntie, unlike Sharma and Shabanu, portrays an obedient woman, with morals. Auntie is traditional, and often criticizes Mama for having no sons in the family. ?If God had blessed you with sons, we wouldn?t have to break our fingers over wedding dresses? (3). Auntie looks down on Shabanu for being ?boy like?. ?A young lady shouldn?t go with her headdress uncovered. You?re too old to act like a boy? (33). Mama is obedient as well. Mama slaps Shabanu as a consequence to non-traditional views. Mama accepts that Dadi takes care of the ?manly? problems such as the selling of the camels. Being the man, Dadi also takes care of the dangerous situations, like getting grandpa after the sandstorm.